The present invention concerns a filtering module, such as a micro-and ultrafiltration module comprising a bundle of tubular inorganic membranes, and in particular to a sealing ring for use with such membranes.
Because of their high levels of resistance to physico-chemical stresses, membrane modules are being increasingly used for filtering various industrial fluids.
These modules are described in a large number of publications and patents, e.g., in Trulson et al U.S. Pat. No. 3,977,967, the disclosure of which is incorporated by reference herein.
One prior art filtration module of this kind is shown in FIGS. 1-3. The filtration module 1 is composed of a cylindrical housing 2, inside of which is housed a multiplicity of tubular inorganic membranes 3, 3a, 3b, etc., arranged parallel to each other in a bundle extending through at least two perforated support plate assemblies located at both ends of the housing which hold the membranes in longitudinal position.
Each support plate assembly comprises a backplate 4 (or 4a), an inner plate P1, and a sealing plate 7 (or 7a). The backplate 4 (or 4a) is bored with as many holes 5, 5a, and 5b, etc. as there are membranes. The sealing plate is formed of an elastomer having a Shore A hardness value less than 60. Each membrane 3, 3a, 3b, etc., passes through the corresponding hole 5, 5a, 5b, etc., of the backplate, through a corresponding hole 6, 6a, 6b, etc., drilled through the elastomer sealing plate 7 (or 7a), and though a hole 30a, 30b, 30c, etc., drilled through the inner plate.
Threaded rods 8 are arranged around the inner periphery of the housing 2. The sealing plate 7 (and 7a) and the backplate 4 (and 4a) are attached to these rods, through holes 9 and 10 drilled respectively in the backplate and sealing plate. The assembly of plates is tightened by means of nuts 11. A sealing ring 12 (and 12a) is arranged on the head of the module. The piping/module unit is locked in place by a collar 13, 13a or by a system of flanges.
FIG. 3 illustrates a membrane 3 extended through the holes in the support plate P.sub.1, the sealing plate 7, and the backplate 4.
The filtration module 1 functions in the following way:
The fluid to be treated enters in the direction of the arrow F.sub.1 and emerges at the other end of the module, in the direction of the arrow F.sub.2.
The permeate circulating on the outside of the membranes 3 and to the inside of the housing 2 re-emerges through openings 14, 14a in the direction of the arrows F.sub.3 and F.sub.4.
In filtration modules of the type shown in FIGS. 1, 2, and 3, the delicate part is the sealing plate 7, 7a. This part is of crucial importance, since it provides fluid-tightness first between the permeate circulating inside the housing 2 and to the outside of the membranes 3, and second, the residue circulating inside the membranes through the module and which flows to the ends of these membranes. This sealing plate must be sufficiently soft to allow proper fluid-tightness to occur. However, in the case illustrated in FIG. 3, it happens very frequently that, during rises in the temperature of the residue and under the effect of the compression exerted on the sealing plate 7 by the plates 4 and P.sub.1, portions 21, 22 of the sealing plate may tend to be extruded or squeezed longitudinally into clearances 23, 23a formed between the membrane 3 and the plates 4, P.sub.1, respectively, as shown in FIG. 3.
These rises in temperature of the residue may reach approximately 130.degree. C. during steam sterilization of the membranes, for example, or in certain industrial processes requiring a high temperature of more than 100.degree. C. This extrusion of the sealing plates 7, 7a and the relative motion between the membranes and the housing 2 during expansion causes deterioration of the sealing plate and, consequently, the loss of fluid-tightness.
Moreover, the compactness of the ultrafiltration modules and the large dimensional tolerances of the tubular mineral membranes do not make it possible either to decrease clearance or to use anti-extrusion rings to enclose the sealing plates 7, 7a.
Although the above-described extrusion phenomenon could be presented by using sealing plates 7, 7a of a sufficiently high level of hardness, the resulting diminished flexibility of the sealing plate may eliminate the fluid-tightness of some or all of the membranes in the module.
Therefore, it would be desirable to prevent the extrusion phenomenon without eliminating the fluid-tight sealing action.